1. Field of the Invention
The present invention relates to a method of and a system for controlling a cooling line or installation and, in particular, a cooling line of a mill train for rolling steel sheets and strips.
2. Prescription of the Prior Art.
In addition to ever increasing requirements to the precision of geometrical measurements, to the quality of the surfaces, and to the mechanical properties of hot rolling strips, there exists simultaneously a desire to increase the flexibility of production plants for producing a multiplicity of different steels. Therefore, there exists a need in automatically operated cooling installations which would insure precise temperature conditions and different cooling strategies, i.e., different cooling processes and which, at the same time, are characterized by high flexibility and insure production of high quality steels. In order to meet these requirements, the process optimization and control methods, which are presently used for the automatization of cooling lines for laminar hot rolled strips, are based generally on mathematical process models.
The conventional methods are based on a classical concept of modeling of an entire system in a form of ideal strip points. The exchange of a strip point with the environment by heat conductance, convection, radiation energy is taken into account during modeling of a strip point.
In addition, inner energy is generated as a result of structural transformations. For modeling of strip points in the strip thickness direction, an equation for an unsteady one-dimensional heat conductance is solved by using the Fourier equation. As geometrical limits of the model, the location of the finishing train pyrometer, i.e., an entry location of an ideal imaginary strip point into the cooling line, and the location of the coiler pyrometer are used. Between these two locations, local adjusting points of the strip temperature are adjusted.
Two types of models are generally used: according to one type, the process model is incorporated into a control circuit, according to other type, the process model is separated from the control circuit. In the second step before the to-be-cooled strip enters the cooling line, the adjusting system of the cooling line is set up, with the feed forward and feed backward control during rolling serving for adjusting the remaining disturbance variables and a unprecise set-up.
In both cases, a separate strip section is divided into segments which are tracked during their passing through the cooling line. The obtained process and adjusting signals are associated with respective segments.
After a segment reaches a coiler pyrometer, in the first case, a reverse calculation of the segment is conducted with the aid of the process model. The difference between the measured and calculated coiler temperature is adapted and is taken into consideration for a following adjustment of the adjusting system in accordance with actual process conditions (temperature of the finishing train, strip speed, etc. . . . ). These calculation sequence is repeated cyclically during the rolling process.
The model adaptation serves for increasing the predicted precision of the cooling model. The results of the calculation of a model are constantly compared with actual, measured results of cooling, and error minimizing its conducted.
A serious drawback of this classical concept consists in that because of a need to integrate the strip segments, a large number of data need be produced and processed. In addition, the adjusting system of the cooling installation or line, e.g., the local distribution of the cooling water and the number of actuated cooling apparatuses, cannot be controlled with a sufficient speed and a sufficient flexibility. There exists a danger of undercooling or overcooling of the strip section when the strip speed abruptly changes.
Accordingly, an object of the present invention is to provide a method of and a system for controlling a cooling line, in particular, a cooling line for a milling train which would insure rapid and automatic control process, with reducing expenditures associated with collection and processing of data.